Increasing energy access and energy security are both seen as key actions for reducing poverty thus contributing to the Millennium Development Goals. Access to modern energy services such as electricity or liquid fuels is a basic requirement to improve living standards. One of the steps taken to increase energy access and reduce fossil fuel dependency is the production of biofuels, especially because biofuels are currently the only short-term alternative to fossil fuels for transportation. However, despite the fact that first generation biofuels (i.e., land-based biofuels produced from agricultural feedstocks) can also be used as food or for feed purposes, the possible competition between food and fuel makes it impossible to produce enough first generation biofuel to offset a large percentage of the total fuel consumption for transportation.
Indeed, land-based biofuels are limited by available suitable agricultural acreage to support plant feedstock growth without direct competition with food feedstocks, rain forests, or other important land environments. Table 1 below shows the respective yields per hectare that can be expected for various commercially grown land-based biofuel crops.
TABLE 1Typical oil yields from the various biomass sources in ascending orderS.N.CropOil yield (l/ha)1Corn1722Soybean4463Peanut1,0594Canola1,1905Rapeseed1,1906Jatropha1,8927Karanj (Pongamia pinnata)2,5908Coconut2,6899Oil palm5,95010Microalgae (70% oil by wt.)136,90011Microalgae (30% oil by wt.)58,700Source: Chisti [2007]; Lele [http://www.svlele.com/karanj.htm]; http://journeytoforever.org/biodiesel_yield.html
Table 1 also shows the high yield per hectare for microalgae. In fact, microalgae represents orders of magnitude higher production per hectare potential over land-based biomass crops currently used for biofuel production. Thus, in recent years, biofuel production from algae has been a focused attraction as a possible alternative to fossil fuel consumption and its alternative land-based biofuel production. Algae have a number of characteristics that allow for production concepts that are significantly more sustainable than their fossil fuel and land-based biofuel alternatives. These include, but are not limited to, high biomass productivity, an almost 100 percent fertilizers (nutrients required for growth) use efficiency, and the possibility of utilizing marginal, infertile land, salt water, waste streams as a nutrient supply and combustion gas source to generate a wide range of fuel and non-fuel products.
For example, algae are very efficient at converting light, water, and carbon dioxide (CO2) into biomass in a system that does not necessarily require agricultural land. In fact, depending on the concept, the water can be salty and the nutrients can come from waste streams. Depending on the species and cultivation conditions, algae can contain extremely high percentages of lipids or carbohydrates that are easily converted into a whole range of biofuels including biodiesel or bioethanol. In addition, the remaining biomass may be used in a number of non-fuel applications including those in the chemical, agricultural, and paper industries. Furthermore, another competitive advantage of algal biofuels is that their development can make use of current fossil fuel infrastructures. Thus, algae-based products can serve as an alternative to a wide range of products that are currently produced from fossil resources or land-based agriculture without requiring high quality land and, in some cases, without requiring fresh water, with CO2 as the only carbon input.
In spite of this potential, in December 2012, a review committee of the National Academy of Sciences (NAS) concluded that the scale-up of algal biofuel production sufficient to meet at least five percent of the United States demand for transportation fuels, which was 784 billion liters in 2010, would place unsustainable demands on energy, water, and nutrients with current technologies and knowledge. The NAS report had several categories of concern with respect to the potential sustainability concerns for large-scale development of algal biofuels. The most serious concerns include (1) the quantity of water (fresh water or saline water) required for algae cultivation and the quantity of freshwater addition and water purge to maintain the appropriate water chemistry, especially in open-pond systems and arid regions, (2) supply of the key nutrients for algal growth—nitrogen, phosphorus, and CO2, (3) appropriate land area with suitable climate and slope, (4) energy return on investment, and (5) GHG emissions over the life cycle of algal biofuels. Other less pressing concerns discussed in the NAS report include, but are not limited to, the presence of waterborne toxicants in cultivation systems that use flue gas as a source of CO2 or wastewater as a source of culture water and nutrients, particularly if fertilizers or feedstuff are to be produced as co-products, the effects from land-use changes if pasture and rangeland are to be converted to algae cultivation, the air-quality emissions over the life cycle of algal biofuels, the potential effects on local climate, the potential alteration of species composition in receiving waters, the effects on terrestrial biodiversity, waste products, and the potential presence of pathogens if wastewater is used for cultivation. Similar issues exist with regard to aquaculture in general when considering long-term sustainability.
Given that the agricultural demand for water in the United States and many areas of the world account for 85 percent or more of consumptive water use, large-scale production of biomass, including algae, has the potential for large regional strain on water systems unless non-freshwater sources are used when possible. The freshwater demands of algal biofuel production will be high if algal biofuels are used to substitute for a significant fraction of annual U.S. liquid transportation fuel consumption, particularly if open ponds are to be used for algae cultivation. If open ponds are used for algae production, as is current “state-of-the-art” technologies, then a significant amount of water will be required to replace evaporative losses from the pond surface and to prevent dissolved salt and silt buildup in biomass cultivation systems. Recent estimates reported by the US Department of Energy suggest that water losses on the order of several hundred liters of water per liter of algal oil or algal biodiesel produced would result from operation of open ponds in arid, sunny regions of the continental United States. Cost effective approaches for reducing evaporative water loss and for dealing with salinity build-up need to be developed. Such approaches will be more important for inland sites where evaporation and salinity build-up are expected to be higher than in coastal marine operational settings that have relatively high humidity. If the algal biofuel industry relies heavily on freshwater resources, it could face a considerable setback as the increased use of freshwater resources becomes less acceptable to the public. Therefore, water recycling and/or use of non-freshwater resources are important to ensuring the social acceptability of the large water requirements for algal biofuel production.
Algae require key elemental nutrients for metabolic maintenance and growth. Photoautotrophic algae use photosynthesis to convert light energy into new algal biomass with an elemental stoichiometry that on average obeys the following equation106CO2+16NO3−+HPO42−+122H2O+18H+C106H263O110N16P+138O2 
The elemental content of algae can be expressed more simply as(CH2O)106(NH3)16(H3PO4)These equations provide a basis for quantitative predictions to be made about the carbon, nitrogen and phosphorous demands of algal biomass production. Providing sufficient and stable supplies of CO2, nitrogen, and phosphorous is essential if algal biofuel production is to be deployed at a commercial scale.
The estimated nutrient requirements for algal biofuel production are substantial. Current estimates suggest that 14-35 kilograms of CO2 is required to produce 1 gallon of algal oil or biodiesel. Additional estimates suggest a nutrient requirement of approximately 0.61 kg N and 0.083 kg P per gallon of algal oil or biodiesel for a 50% oil content algal biomass. If nutrients are not recycled or supplied from waste sources under current cultivation technologies, nutrient requirements of algae for fuels could incur indirect and unintentional impacts on food prices through direct competition for limited fertilizer resources. It will additionally prove detrimental to the algal biofuel industry if it is viewed as a massive sink for nutrients that are in short supply, particularly if it is perceived that they are in direct competition with food producers.
Another major constraint on the future expansion of biofuel production is likely to be the limited amount of land suitable for producing bioenergy crops. The sites where algal cultivation systems can be installed will be constrained by high land cost, agricultural activity, environmental value, and intrinsic cultural value of the land being considered. The diverse set of site-specific factors would have to be carefully matched to the cultivation systems used for algal biofuel production if the essential requirements for successful large-scale algal biomass production (suitable land and climate, sustainable water supplies, and sustainable nutrient supplies) are to be aligned in terms of their geographical location. Meeting all of these requirements in a sustainable and cost-effective manner is extremely limiting to the potential development of commercial biofuel production under current commercial cultivation practices. Optimal sites for commercial-scale algal biofuel production would have either the required resources in close proximity or mechanisms in place to ensure adequate and uninterrupted supplies of these resources.
Innovations that result in reduced resource use along the entire algal biofuel supply chain will remove some of the existing barriers to the development of large-scale, sustainable, and economically viable algal biofuel enterprises. Therefore, a method of cultivation and harvesting algae biomass and aquaculture that embraces and mitigates concerns for large scale implementation is needed. The present invention relates to the algal (aquaculture) production supply chain and systems and methods pertaining to cultivation and harvesting.